Imbalanced Flywheel
Imbalanced Flywheel
(OP)
Apologies for asking a possibly common flywheel question: my car forums of choice are vastly under-qualified to help. My question is twofold: How likely is it that a 23 lb (mild steel?) flywheel turned on a lathe (improper tool) or ground (proper tool) would become out of balance significantly enough to cause the entire driveline to vibrate? How much imbalance would be necessary to cause this situation?
The car is a 2.5L H4 AWD (Subaru WRX).
I recently had my clutch changed at a shop which sublet the flywheel resurfacing to another shop of unknowable quality. The service manager inadvertently informed me that no shops in the area are capable of balancing flywheels of "that size." I assume they must have ground the surface because the clutch does not slip.
I've done a great deal of googling trying to understand the issue better. I don't have access to a vibrations text, only my notes from the class. So I have the equations of motion, but lack the experimental capability to characterize the constants. Ultimately, I'd like to use Shigley's to make some prediction on the increased fatigue life of the crank. (I've yet to apply ISO 1940/1 which was suggested in another forum for predicting amplitude of vibration of a pump rotor.)
Thank you for any information!
The car is a 2.5L H4 AWD (Subaru WRX).
I recently had my clutch changed at a shop which sublet the flywheel resurfacing to another shop of unknowable quality. The service manager inadvertently informed me that no shops in the area are capable of balancing flywheels of "that size." I assume they must have ground the surface because the clutch does not slip.
I've done a great deal of googling trying to understand the issue better. I don't have access to a vibrations text, only my notes from the class. So I have the equations of motion, but lack the experimental capability to characterize the constants. Ultimately, I'd like to use Shigley's to make some prediction on the increased fatigue life of the crank. (I've yet to apply ISO 1940/1 which was suggested in another forum for predicting amplitude of vibration of a pump rotor.)
Thank you for any information!





RE: Imbalanced Flywheel
or assuming a workman-like product (correctly done); possibly a poor installation, such as the flywheel not perfectly seated on the crank, or the clutch pressure plate not perfectly seated (not likely).
Not being 'current' on Subarus, this is a wild guess.
RE: Imbalanced Flywheel
RE: Imbalanced Flywheel
Here is a picture of a WRX flywheel of unknown vintage.
http:/
note the 3 dowels to locate the clutch cover/pressure plate
i'd ask what what was "checked". If the "nothing wrong" did not include indicating the face of the flywheel relative to the mounting flange, then that must be done. In the pic above there is a hint of a shadow that suggests the surface does not touch the benchtop, which would be the case if the crank flange surface is in a recess. If the machine shop just set such a flywheel on the grinder's table it would not reference the proper surface. If the ring gear is what touches table first, a similar un-true surface would result. An adapter (precise ring) is need to "pick up" the correct surface. An experienced or well trained machinist would not grind it improperly because she would (1) use the right adapter and (2) recognize that if the grinder was taking off a lot of material all on one edge there is a problem.
Rather than let the shop take it apart again, I'd make an effort to indicate the flywheel surface with the starter removed, rotating the crank by hand. there could be fore and aft motion within the crank thrust clearance, but if you applied axial pressure to the crank while turning I'd expect to get a meaningful reading. 0.002 inch is OK, 0.020 is not.
Another way to get in trouble is to install the clutch with the dowels missing. then the entire weight of the pressure plate can be offset a mm or so by the clearance between bolts and clutch.
Here is a pic of a subaru crank and flywheel.
http://ww
It looks like there is no register in the FW for the crank flange, and that the pilot bearing might extend into the crank to provide flywheel radial centering
RE: Imbalanced Flywheel
The most frustrating part is that I have no means to verify there was no error in installation. This is coupled with the fact that I have convinced them on the basis of a poor flywheel job to install a brand new flywheel very soon. If they again install the clutch improperly, or it is indeed the clutch itself, I will have egg on my face. It will be months before I have access to the space and tools I'll need to just do it myself.
There is no end of cases of botched flywheel/clutch installations for Subarus, so I'm not looking forward to it.
RE: Imbalanced Flywheel
paraphrasing A. Doyle
(altho he believed in Faries)
"when you have eliminated the impossible, whatever remains, however improbable, must be the truth."
RE: Imbalanced Flywheel
First, there is NO right machine to resurface a flywheel. I've had flywheels done on a nice new Blanchard grinder and I've done them on my old Sears lathe. Never a problem for me, but I always re ck the balance (a balance shop was my racing sponsor, duh!). Still, I see your problem as stated above. Too bad. Scary part when they "took it apart and found nothing". What in heck were they looking for?
Second, the fact that the gearbox was out could open a few other possibilities that could cause "vibrations" because of a "different" position upon re assembly.
Rod
RE: Imbalanced Flywheel
Rod, you raise good points. I had read many horror stories of slipping clutches occurring simply turning the flywheel on a lathe to resurface it on subarus, so I assumed it wasn't the ideal tool for the job.
As for what they were looking for, that's a good question. I'm not sure why they agreed to comp the labor and spend 5 or 6 hours working on my car if they had no plan!
I had absolutely considered the possibility of mounts or crossmembers being "bound." At the time, I was able to remove and replace them at factory specs with brand new harder mounts. This didn't solve the problem, it just changed the frequency of vibration to the rest of the car thanks to the increased mounting stiffness, haha. Unfortunately for my trim and dashboard, the harmonics happen right around cruising RPM now.
RE: Imbalanced Flywheel
Rod
RE: Imbalanced Flywheel
RE: Imbalanced Flywheel
New flywheel clutch or, at least, have them balanced by a REPUTABLE SHOP!
Rod
RE: Imbalanced Flywheel
I can see how a part could be misplaced, or even missed during build up, but How in the world did they ever stab the transmission without aligning the disc with the (missing) pilot bearing? (and it is a ball bearing in the Renault.)
Just blind luck I guess.
RE: Imbalanced Flywheel
1. Does the vibration occur if you bring the engine to the problem revs with the trans in neutral? If not your problem is elsewhere.
2. If it does, put your foot on the clutch and select a gear (this will stop the friction plate from turning) then bring the engine to the problem revs. If the vibration is still there, the problem is in the flywheel or pressure plate. If this is the case:
3. Have the mechanic remove the pressure plate and (if possible) start the engine without the pressure plate fitted. If the vibration is still present it must be the flywheel.
RE: Imbalanced Flywheel
I can just imagine the look on the mechanic's face when this is suggested.
Of course, "it all pays the same", I suppose.
IMHO, if this engine/trans must be split again, the whole clutch, pressure plate, and flywheel group needs to go to a competent clutch/driveshaft shop for inspection & balance. Even if it has to be shipped out.
RE: Imbalanced Flywheel
Thruthefence, this is not possible for the same reason it was not possible to get the balance on the flywheel checked on my 2nd visit: there are no businesses of which I or the service manager are aware with the requisite equipment in the area, and I don't live there. It's my daily driver, so I can't leave it there for weeks waiting for turnaround on my drivetrain. It's a bad situation.
In the event that I am able to make arrangements, perhaps a rental with discount, what companies might you suggest for this service? Or, alternately, where would I go to search for one? The garage is in Mobile, AL.
Thanks!
RE: Imbalanced Flywheel
http://clutchandpowertrain.com/
they are in Mobile, AL
It might be worth a call. They do hot rod stuff, so I would think they could handle a Suburu.
(No financial interest, ect)
RE: Imbalanced Flywheel
Well, I guess none of you have tried that little bit of nonsense. I'm not that smart and I tried it, ONCE !!! Way back when...When I was experiencing some difficulty or another with the clutch/flywheel. NOT A GOOD IDEA! Especially when the ring gear flies off because it was, primarily, secured to the Al flywheel by the six 5/16" cap screws that mounted the pressure plate !!!!!!
Keep that in mind. It was not a pleasant lesson, but a REALLY good and lasting one.
Rod
RE: Imbalanced Flywheel
I think the flywheel's axial (face) runout needs to be measured.
If the unbalance is the result of poor machining it should be corrected before balancing. And, If the runout is less than 0.002 inch or so, flywheel balance is not likely the issue.
If it was mine and especially if I was in a jam I'd rig up the flywheel supported on the ball bearing pilot bearing with a bolt in a vice expecting I could detect gross imbalance of the flywheel, and then clutch assembly . Might have to remove the seals and dilute the grease for greater sensitivity. That would be a good setup to check flywheel face runout too.
"if I can't measure it, how am I going to fix it?"
An internet search for engine balancing came up with this -
Rick's Machine Shop
3210 Dauphin Island Pkwy
Mobile, AL 36605
251-479-1501
Yellow pages topics like "automobile racing and sports car equipment" "engine balancing" "balancing and vibration analysis" are likely to uncover a few sources. I expect any engine rebuilding shop would either have a balance machine, or know who does. Many shops have "universal" arbors that would be able to handle your Subaru flywheel after the pilot bearing is removed.
RE: Imbalanced Flywheel
And Rod, I'm glad you learned that lesson for all of the rest of us!
RE: Imbalanced Flywheel
I ask, because I have a collet chuck on my lathe, with quick change cam lock attachment. When I bought it, I spent considerable time 'indicating' the chuck so it ran perfectly true to the spindle, .001 runout; pretty close for a redneck & a Chinese knockoff chuck. (the lathe itself is quite accurate, a very low time Austrian built Emco-Maier)
when making some parts for a project, I noticed severe runout on the work piece. The runout was .008" or so, three inches out from the business end of the chuck. unacceptable!!
Investigation showed I had missed a small piece of swarf, (trapped between the chuck & spindle) when I swapped the three jaw for the collet chuck. You could hardly see it, it was so small.
my point is, that if a piece of trash is under the flywheel, it is possible to have quite a bit of runout at the clutch surface.
RE: Imbalanced Flywheel
RE: Imbalanced Flywheel
looks like it goes right to here:
"If clutch work recently done,
problem could be related to
the clutch. Verify proper
clutch was installed."
RE: Imbalanced Flywheel
Now, that is for an engine built from a balanced crank and a balanced pulley and a balanced flywheel, and we still ended up balancing the flywheel plane for EVERY engine after assembly.
So, fully machined parts assembled to a balanced crank can and will cause detectable vibration. Whether they would cause destructive levels of vibration is another thing entirely.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Imbalanced Flywheel
Can you explain why so many people manage to get away with machining their FW without noticeable issues? In my case, I would absolutely venture that the fully machined part was fully machined improperly considering that the vibration has proven destructive: a recent development is a pretty loud intermittent squeaky sound in low gears in low rpm ranges. It's probably a bearing. Since I don't know which and subsequently don't have the part, I expect this will become a problem in the future. I can only guess at what will happen when it fails.
RE: Imbalanced Flywheel
It actually takes fairly sloppy machining technique to get it wrong. Any machinist who cares more than a jot, will observe the sound at the beginning of the grinding operation. Any runout will be evident as an intermittent sound.
RE: Imbalanced Flywheel
Plenty of cars' flywheels are retained and secured by shrink fit and a shoulder to resist the initial slam of the bendix.
No pressure plate involvement at all.
Vintage US - http://
Anglophile - http://d
Not sure about this trendy mod dual mass set up - htt
mark twain said something about a cat that having once sat upon a hot stove would never risk sitting on a cold one either
RE: Imbalanced Flywheel
So, fully machined parts assembled to a balanced crank can and will cause detectable vibration."
What you say is what I understood to be true previously. I'm interested to hear Greg's reasoning.
Tmoose, I'm not sure how Rod's situation would come to pass, either. My flywheel is a single machined steel body bolted onto the crank.
RE: Imbalanced Flywheel
Dan T
RE: Imbalanced Flywheel
Your second link is to a stock Mini flywheel. Even that is old fashioned compared to the SIX Lb. units we race with today. Certainly requires a definite "attitude adjustment" when it comes to making one of these little dears work properly.
Rod
RE: Imbalanced Flywheel
My comment was assuming the situation under discussion where a well-balanced motor has the flywheel removed, machined and refitted. It should remain well-balanced if the machining was accurate.